1. Field of the Invention
This invention relates to flying discs of a type thrown by hand in a way that causes them to have both forward and angular momentum. In particular, the invention relates to providing such discs with at least one surface that interlocks with a properly shaped surface of a weight ring to hold the weight ring firmly in place in spite of the typical, severe jolts to which the disc is subjected in use.
2. The Prior Art
The type of disc with which this invention is concerned has a lightweight but strong central membrane, or web, with a molded, outer, annular rim curved away from the web to form a more or less cylindrical outer wall. Together, the web and the rim have the form of a shallow dish. The edge of the rim has a rounded cross section resembling an air foil. The thickest part of the air foil measured in the usual direction of measurement of thickness of an air foil, that is, perpendicular to the chord, and in this invention approximately parallel to the plane of the web, is not immediately adjacent the edge farthest from the web but is perhaps one-third or so of the distance from the edge to the web. The inwardly facing surface of the air foil section of existing discs is substantially flat in cross section and defines a generally cylindrical surface. The annular rim consists primarily of a suitable thermoplastic material, such as polyethylene, and the cylindrical configuration of the facing surface of the rim makes it easy to remove the annular ring from the mold.
Interest in the type of discs with which this invention is concerned is based on their flight characteristics. The shape of the disc gives it lift, when properly thrown, so that it does not simply sink to the ground as would a smooth, spherical ball of the same mass thrown with the same force. Some enthusiasts try to throw such a disc so that if flies as far as possible, and contests are held for that purpose. A more casual and probably more common usage is for enthusiasts to throw a flying disc of the shallow dish type back and forth to each other, either keeping the disc in the air or bouncing it off the ground somewhere between the players. Another way of enjoying the discs is for players to try to cause them to follow unusual, curved flight paths. Still another thing that enthusiasts do with the discs is to "tip" them, which is defined as hitting the under surface of a spinning disc in the center by means of the player's finger tip, knuckle, or toe. The stress on a disc due to tipping it can be severe.
As might be expected, the various requirements of different players have led to different designs of such discs. A main difference is in the weight, which may be as light as about 110 grams or as heavy as about 180 grams. Wind conditions have an important bearing on the particular disc an enthusiast will select at a given time; heavier ones are usually preferred in windy weather.
Although polyethylene does not shatter as would a more brittle material, it can be nicked, particularly when it is bounced off a paved surface or flies into an abrasive surface. The resulting projections from the originally smooth surface can make the disc painful to catch.
The flight characteristics of a flying disc are affected by the air foil and surface configuration, especially on the convex surface. Such discs are normally thrown with the rim extending downwardly from the plate, which is equivalent to saying that the convex surfaces face partially outwardly and partially upwardly. For this reason the convex surfaces of the ring will be referred to as the upper ones and the concave and inwardly facing surfaces as the lower ones in the following description.
It has been found desirable to mold spoilers in the upper surface of a flying disc near the outer part thereof to reduce air drag and improve precessional qualities of the disc. U.S. Pat. No. 3,359,678 to Headrick describes concentric ridges that act as spoilers to interfere with air flow.
Other publications that describe characteristics of Frisbees are the book FRISBEE by Stancil E. D. Johnson, M.D. published by Workman Publishing Company, N.Y., and a paper entitled "Adaptation of the Frisbee Flight Principle to Delivery of Special Ordinance" by G. D. Stilley of Honeywell Incorporated and D. L. Carstens of the Naval Ammunition Depot, Crane, Indiana, and presented at the AIAA 2nd Atmospheric Flight Mechanics Conference at Palo Alto, Calif., Sept. 11-13, 1972 (AIAA) Paper No. 72-982).
My U.S. Pat. No. 4,204,357 and copending application Ser. No. 154,484 describe discs that include generally radial spoilers and a structure comprising an annular ring with an air foil and a central web of lighter weight than the usual polyethylene molded center that the web replaces. It is also taught that the moment of inertia of the disc can be further increased by adding weight rings inside or outside of the rim at the outer perimeter of the annular ring.